The present invention is directed to an improved inspection system which utilizes penetrating radiation.
Conventional inspection systems which employ penetrating radiation may use one of two methods to inspect objects. In both cases, illumination by penetrating radiation is provided in a scanning plane, and a conveyor carries the object past the scanning plane. The illumination may be a planar beam forming a triangular fan, or a flying spot. Such illumination may be formed so that one extreme end thereof is tangent to the belt while the other extreme end of the illumination is above the top of the object, which is a so-called "horizontal system". Alternately, the illumination may emanate from above or below the conveyor, a so-called "vertical system".
One problem in a "vertical system" is that the image formed by the penetrating radiation is substantially deteriorated because the radiation beam must penetrate the conveyor belt at least once. Although all such systems "erase" the transmission image of the conveyor belt, the belt absorbs a substantial fraction of the radiation which forms the low energy portion of the radiation beam. The image of thin objects is formed principally by these low energy photons because only low energy photons are significantly absorbed by thin objects, and this is particularly true of organic or low atomic number materials.
A more important problem in the inspection of thin objects concerns the scatter image. Thus, when thin objects are inspected with backscatter radiation, it has been found that the signal which is detected by the backscatter detector is so deteriorated by the presence of the conveyor belt that it may not even be useful.
An additional concern in the inspection of objects, and particularly heavier objects than referred to above, is that it is desirable to provide a display which images such objects so that they appear to the viewer to be three dimensional. That is, objects which are inspected by security systems are frequently six sided objects which are substantially in the shape of rectangular solids, for example, suitcases and cargo boxes. However, prior art inspection systems typically provide a display of such objects which is primarily a two dimensional shadowgraph, wherein some of the sides and edges of the object are not even seen. Additionally, in such prior art displays, it may be difficult to see items which are located or packed behind other items through the thickness dimension of the object, as well as items which have a significant geometric shape which lies along the thickness dimension. This can be a major disadvantage, as in many actual inspection situations an operator has only a few seconds to determine whether each object presents a security threat. A display projection which appears to be three dimensional wherein the viewer clearly sees all six sides of the object, as well as items which are located behind other items through the thickness dimension of the object would be more useful and effective to discover hidden contraband.
It is therefore an object of the present invention to provide the ability of inspecting thin objects with penetrating radiation.
It is a further object of the invention to provide the ability of inspecting thin objects with radiation which is backscattered by the objects.
It is still a further object of the invention to provide a display projection of multi-sided objects, which appears to be three dimensional, and in which the contents of the object can be clearly seen.